WASHINGTON: Migrants entering the US without documents as pandemic-era controls lift Thursday face long-term bans and possible prosecution, a top official warned.

"Our borders are not open," Homeland Security Secretary Alejandro Mayorkas said, hours before the United States implements a tough new immigration policy.

Mayorkas stressed that the new rules under the Title 8 law pose tough consequences to border crossers, even those requesting asylum.

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"If anyone arrives at our southern border after midnight tonight, they will be presumed ineligible for asylum and subject to steeper consequences for unlawful entry, including a minimum five year ban on reentry and potential criminal prosecution," Mayorkas said.

The Title 42 policy, put in place in January 2020 under a coronavirus public health emergency, will be lifted at midnight Thursday.